Maintaining distribution of load between leonard drives



April 9, 1929- v A.' K. BUSHMAN 1,708,870

MAINTAINING DISTRIBUTION OF LOAD BETWEEN LEONARD DRIVES Filed Sept. 28, 1926 Inventor-'1 Andrew KJSus'nman His At orney.

Patented Apr 9, 192% unites rnssvo ANDREV K. BUSI-IMAN, OF GAK PARK, ILLTNOIQ, ASSIGNOR T0 GEHERAL ELECTRIC COMEANY, A CORPQR-ATION 015 NEW' "YORK.

MAINTAINING DISTRIBUTION OF LGAD BETWEEN LEONARD DRIVES.

Application filed september 28, 1928.

My invention relates to the distribution of load between Leonard drives, and in particular to the distribution oi the load in such systems in which the separately excited motors of the drives are connected to a common load.

The invention has a particular application in double unit rolling mill drives wherein it is desirable to 'ye load by at least two motors and to provide a generator for supplying: the current for each motor armature. In such drives, it the two motor armatures are connected in series with the two generator armatures in a local circuit, because of considerations of safety to the operators and other problems which arise by reason of the relatively high voltage, provision must be made to insure that the potential across any two points of the system will not be greater than the potential of one generator armature. One way of accomplishing this is to alternate the motor armatures and the generator armatures in the local circuit; My invention provides another way of insuring that the maximum potential of the system will not be greater thanthe armature potential of one generator, and has certain advantageous features, as will be pointed out hereinafter, whereby there will be automatically main tained a predetermined distribution of the load between the motors;

In accordance with my invention, each motor and generator is connected in a Leonard system, the armatures of the motor and generator of each set being connected in a local circuit. 1 A common conductor is provided as a connection between said local. circuits. The excitation of the generator of each set is governed by two field windings, the energizations of which are adjusted so that the two windings normally neutralize each other. One winding is energized in accordance with the current in the local circuit which the associated generator armature is included and the other winding is energized in accordance with the current in said common conductor. The net result of the flux set up by the'two windings will be such that, upon an unbalance the loads ofthe motors, the excitation of each generator will be varied in such a direction and value that the predetermined distribution of the loads will be promptly reestablished.

For a better understanding of the invention, reference is had to the accompanying Serial: No. 133,1 55.

drawing which shows a simplified system in accordance with the invention.

The system oi control comprises two motors having armatures 1G and 11, respectively, and field windings 12 and 13, respectively, the field windings being arranged to be energized from the separate source of supply 14. The motor having armature 10 and field 12 is supplied with armature current from the generator armature 15, which is connected in a local circuit with the armature 10. The motor having armature 11 and field 13 is connected in a local circuit wi h the armature 16 of another generator which supplies the armature current for this particular motor. The generator field windings 17 and 18 are connected in series as shown, and are supplied with energy from the source 14: under the control of controlling means including the reversing and speed varying controller c and the directional. contactors l9 and 20. The separately excited generator l517 and the separately excited motor 1012 form in effect a Leonard system and this Leonard system forms one set of the machines oif which the other set comprises the separately excited generator l618 which forms a Leonard drive with the separately excited motor 11-43 The connection 21 terms a common conductor between these two sets of Leonard systems and with the potentials of the generator armatures as indicated the current through this common conductor will be the sum of the currents through the outside conductors 22 and 23.

The distribution of the load between the two sets of similar Leonard drives is eiiected in response to the relation between the current in each of the outside conductors 22 and 23 with rela ion to the common conductor 21. This distrib tion of the load is preferably effected by means oi a set of field. windings for each of the generato s The field winding 24 for the le 't-hand Leonard drive is connected in shunt relation with a portion of the conductor 21 so as to be energized responsively to the cm ent oi: this conductor and the field win ding); is connected in shunt relation with a portion of the conductor 22 so as to be or iZed in accordance with the curren th conductor. The energication oi field windings is adjusted so that the lint s up thereby normally neutralize each ct or when there is the predetermined distribution of load between the two motors. l Vhcn this predetermined diswill increase, whereas the flux set up by the tribution of the load is unba. ccd ll lofield winding 2', ot the right-hand generator windings will be energized a will decrease. The resultant flu or the ield and at a value such that the resn will be in the proper direction an proper value so as to vary the exert n the generator 15-h? and promptly correct for the departure JllC predeterm ned relation The gcncr: 'or l(l----'l8 has a similar set of field windings Q and 527, the field winding 26 being connected so to be energized in accordance with the current of the conductor .il and the field winding 2'? being connected so as to be energize in accordance With the current in conductor The two motors are indicated as being connected to a common load 28.

As thus constructed and arranged and with the various parts in their :pecl positions as shown in lil drawing, the

ation oi my invention is 7 follows: A;

that it is desired to operate the load 93 in one-direction, the controller 0 will be tn" iwn trom its off position, that indica e drawing, to energize eithcrthe revt duetor 19 or 20, depending upon t tion selected. Assume that the has been thrown to the right to its controller first operative position :The field contactor 19 will be energized to close and cause the field windings 17 and 18 to be energized from tile separate source of supply 1 lthrough the speed varying resistor 29. The controller 0 is advanced through its various operative positions, the resistor is shunted section by section and the load'28 will be accelerated by reason of the tact that the voltages of the t. *0 generators will increase, In case the opposite direction oi"? rotation for the driven load is desired, the controller will be thrown to the left, thereby energiz ng the reversing field contactorQO and causing the flow of current through the generator held windings l? and 18 to be in the opposite direction.

The current flowing through the various field windings 2% and 25 of the one generator, andthc field win ,ings 9,6 and 2'? of the other generator, will be adjusted so that when the load is distributed as desired between the two sets of Leonard drives, the resultant flux of the field windings 52 i; and 25 of the one generator will he nil and the resultant flux of the field windings 26 and 27 ot the other generator will also be nil. In case there is a variation from this distribution of load, there will be a variation in the energization of these field windings and this variation will beef such a magnitude and in such a direca reestablislnnent of the pretion as to ehect determined relation between the loads carried by the two sets of Leonard drives. Thus, ifthe current in the conductor 22 should increase and the cnrrent in the condnctor 23 simultaneously decrease, the flux set up by the field winding 25 of the lettdiand generator windin and will now be oi. a value which is substantially proportional to the outot-balance load and this tlux will be in such a direction as to oppose the flux set up by the field winding 17 and thereh reduce the generated pote tial oi the lclthand generator. The ticld v 1:, Inn 24'; il predominate in the right-hand Leona and there will be a resultant fin; a es set up by field windings 26 an 1 willv be in a direction to a i set up by field winding 18. This w o an increase of the potcin tial of the right-hand and cause the motor 1113 to to greater share of the driven loac. From the example which has been just given, those skilled in the art will readily understand the principles of the invention. l Vhile T. have shown the controlling field winnings and 25 and 2627 as regulating the potential of their respective generators, I would have it understood that my invention is not necessarily limited to the control of the load distribution by the gcnerator potential, but is likewise applicable to the control of the motors directly by varying the excitation provided by the field windings 12 and 13.

What I claim as new and desire to secure by Letters Patent oi the United States is 1. In combination in a Leonard system, two similar sets of machines, each set including a separately excited generator and a separately excited motor having their armatures in a closed local circuit each part of which carries at least tull armature current, and excitation controlling means for a machine of each set for automatically maintaining a predetermined relation between the armature currents of said motors, the said means being connected with the system to respond differentially t0 the direction and the value of the current in the local circuit of the other set and the armature current of the motor of the set.

2. In combination in a Leonard system, two similar sets 01 machines, each set including a separately excited generator and a separately excited motor having their armatures in a closed local circuit each part of which carries at least tull armature current, and excitation controlling means for each generator energized differentially in response to the current in the local circuit of the other set and the current through the generator armature for automatically maintaining a predetermined distribution of load between said motors.

3. In combination in a Leonard system, two similar sets of machines, each set including a separatel excited generator and a separately excited motor having their armatures in a local circuit, the said motors being connected to a common load, a field winding for each generator energized responsively to the sum of the currents in said local circuits, and a second field winding for each of said generz tors energized responsively to the current through the generator armature, said second field windings being differentially wound with respect to said first field windings for automatically maintaining a predetermined distribution of load between said motors.

at. In combination in a Leonard system, a set of machines comprising a separately excited generator and a separately excited motor having their armatures included in a local circuit, a second similar set of machines, the said motors being connected to a common load, the local circuits of said sets having a common conductor which carries the sum of the current in the local circuits, a field winding of each generator energized responsively to the current in said conductor, and a field winding for each generator energized responsively to the armature current of the associated generator and difierentially wound with respect to the first said field winding to maintain a predetermined distribution of the load between said motors.

5. In combination in a Leonard system, two similar sets of machines, each set including a separately excited generator and a separately excited motor having their armatures in a local circuit, the said local circuits having a common conductor and the generator armature terminals connected to said conductor having the same polarity, and means for ,maintaining a predetern'iined distribution of the load between said generators, the said means including a field winding for each generator connected in shunt with a portion of said conductor, and another field winding for each generator difierentially wound with respect to said first winding and connected in shunt with a portion of said local circuit which carries only the armature current of said generator.

In witness whereof, I have hereunto set my hand this 25th day of September, 1926,

ANDREW K. BUSHMAN. 

